1. Technical Field
The present invention relates to plate-shaped glass fragmentation testing method and device, image pickup method for glass test, and image signal processing method, which are used for quality assurance in the production of plate glass.
2. Background Art
Most of windowpanes for automobiles and so on are made of tempered glass, which has had compressive stress applied to surfaces thereof to improve resistance to tensile stress. In the production of such a kind of plate-shaped glass, a fragmentation test or a similar test has been carried out as a quality assurance test.
The fragmentation test for tempered glass is prescribed in JIS standard (JIS R 3212-1992), ECE standard (E6) or another standard. The fragmentation test is a test wherein test glass is fragmented by applying an impact shock to a certain portion thereof with a punch, the number of fragments in a region with the coarsest fragment included and in a region with the finest fragment included are calculated, and the area of the greatest fragment and the length of the longest fragment in that region are measured to see whether the test glass meets desired specifications, or not.
For the calculation of the fragments or another purpose, a measuring method has been adopted wherein the image of fragmented test glass is exposed on photosensitive paper to obtain an image as a blueprint (hereinbelow, referred to as a blueprinted image), and the measurement is conducted utilizing the blueprinted image. In the measuring method, all operations including the setting of selected regions and the calculation of the number of the fragments have been manually carried out based on the blueprinted image. The conventional measuring method has required considerable labor in the calculating operation for counting the number of the fragments and another operation.
As an example of systems to improve the operability in the fragmentation test, xe2x80x9cAutomated calculating system for the ECE fragmentation testxe2x80x9d Ford Motor Co. (GLASS PROCESSING DAYS, 13-15, Sep. 1997) discloses a technique that the calculating operation for counting the number of the fragments and another operation in the blueprinted image are automatically carried out by a computer. According to this automated calculating technique, there is no need for an operator to manually count the number of the fragments, reducing the number of the steps required for the calculating operation.
Since the measurement of the number of the fragments and another operation have been manually made by an operator in the conventional manual measuring method for the fragmentation test as spreaded area, the conventional manual measuring method has created a problem in that the calculating operation in the fragmentation test requires many steps and much labor cost.
On the other hand, the automated calculating technique stated above can reduce the number of the required steps in comparison with the manual calculating operation. However, the automated calculating technique requires a step to prepare a blueprinted image and a step to take a picture of the blueprinted image since the automated calculating technique has carried out the measurement using the blueprinted image as in the conventional manual measuring method.
The present invention has been proposed from this viewpoint, and the present invention has an object to provide a plate glass fragmentation testing method and device, an imaging method for glass test, and an image signal processing method capable of directly picking up an image of test glass and dealing with a calculating operation of the number of fragments and another operation in automated fashion thereby to carry out a fragmentation test with good operability and high precision.
The present invention provides a plate-shaped glass fragmentation testing method characterized in that the method comprises a glass image pickup step for providing a sheet screen in substantially close contact with one of sides of plate-shaped test glass, fragmenting the test glass, and irradiating light for image pickup to the other side of the test glass to electronically and directly pick up a projected image of the fragmented test glass from the side of the test glass with the screen provided; and an image processing step for performing a calculating operation to calculate the number of fragments of the test glass, the area of the greatest fragment and the length of the longest fragment in at least a selected region based on tone image signals of the test glass thus obtained.
By directly picking up the test glass according to this method, a clear tone image can be provided, and operations, such as calculating the number of the fragments, can be automatically performed based on the tone image signals, allowing a fragmentation test to be carried out with good operability and high precision.
It is preferable that in the image processing step, a binarizing operation is performed to binarize the tone image signals of the test glass while modifying threshold values according to brightness of a background in the tone image, and the calculating operation is performed based on the binarized image signals after the binarization.
It is further preferable that in the binarization, the tone image of the fragmented portions with a cracked portion of the glass eliminated is used as a threshold value distribution image for binarization, and the binarization of the tone image signals is performed according to the brightness of the background based on the threshold value distribution image.
The present invention also provides a plate glass fragmentation testing method characterized in that the method comprises a glass image pickup step for electronically and directly picking up plate-shaped test glass in fragmented fashion, a binarizing step for binarizing tone image signals of the test glass thus obtained while modifying threshold values according to brightness of a background in the tone image, and a calculating step for calculating the number of fragments of the test glass, the area of the greatest fragment and the length of the longest fragment in at least a selected region based on the binarized image signals after the binarization.
By this method, the tone image signals can be binarized in optimum fashion according to brightness of a background in the tone image obtained by directly picking up the test glass, and operations, such as calculating the number of the fragments, can be automatically performed based on the binarized image signals, allowing a fragmentation test to be carried out with good operability and high precision.
It is preferable that in the glass image pickup step, a sheet screen is provided on one of sides of the test glass in substantially close contact, and light for image pickup is irradiated to the other side of the test glass to pick up a projected image of the test glass from the side of the test glass with the screen provided.
More preferably, the plate-shaped glass fragmentation testing method further comprises a display step for displaying at least the tone image of the test glass and results of the calculating operation.
It is preferable that the plate-shaped glass fragmentation testing method further comprises a storage step for storing at least data of the tone image of the test glass and data of the results of the calculating operation on a recording medium in correlated fashion.
The present invention also provides a plate-shaped glass fragmentation testing device characterized in that the device comprises an image pickup unit including a light source to producing light for image pickup to irradiate fragmented plate-shaped test glass from one of sides thereof, a sheet screen provided on the side of the test glass remote from the light source in substantially close contact, and an image pickup means for electronically and directly picking up a projected image of the test glass from the side of the test glass with the screen provided; and an image processing unit including a calculating means for calculating the number of fragments of the test glass, the area of the greatest fragment and the length of the longest fragment in at least a selected region based on tone image signals of the test glass thus obtained.
By directly picking up the test glass according to this arrangement, a clear tone image can be provided, and operations, such as calculating the number of the fragments, can be automatically performed based on the tone image signals, allowing a fragmentation test to be carried out with good operability and high precision.
It is preferable that the image processing unit includes a binarizing means for binarizing the tone image signals of the test glass while modifying threshold values according to brightness of a background in the tone image, and the calculating means performs the calculation based on the binarized image signals after the binarization.
It is further preferable that the binarizing means utilizes the tone image of the fragmented portions with a cracked portion of the glass eliminated as a threshold value distribution image for binarization, and the binarization of the tone image signals is performed according to the brightness of the background based on the threshold value distribution image.
The present invention also provides a plate-shaped glass fragmentation testing device characterized in that the device comprises an image pickup means for electronically and directly picking up plate-shaped test glass in fragmented fashion, a binarizing means for binarizing tone image signals of the test glass thus obtained while modifying threshold values according to brightness of a background in the tone image, and a calculating means for calculating the number of fragments of the test glass, the area of the greatest fragment and the length of the longest fragment in at least a selected region based on the binarized image signals after the binarization.
By this arrangement, the tone image signals can be binarized in optimum fashion according to the brightness of the background in the tone image obtained by directly picking up the test glass, and operations, such as calculating the number of the fragments, can be automatically performed based on the binarized image signals, allowing a fragmentation test to be carried out with good operability and high precision.
More preferably, the plate-shaped glass fragmentation testing device further comprises a display means for displaying at least the tone image of the test glass and results of the calculation.
It is preferable that the plate glass fragmentation testing device further comprises storage for storing at least data of the tone image of the test glass and data of the results of the calculation on a recording medium in correlated fashion.
The present invention also provides an image pickup method for glass fragmentation test characterized in that the method comprises a step for providing a sheet screen in substantially close contact with one of sides of test glass, a step for irradiating light for image pickup to the other side of the test glass, and a step for electronically and directly picking up a projected image of the test glass from the side of the test glass with the screen provided.
The present invention also provides an image signal processing method for glass fragmentation test characterized in that the method comprises a step for inputting tone image signals obtained by picking up test glass, a binarizing step for binarizing the tone image signals of the test glass thus obtained while modifying threshold values according to brightness of a background in the tone image, and a calculating step for calculating the number of fragments of the test glass, the area of the greatest fragment and the length of the longest fragment in at least a selected region based on the binarized image signals after the binarization.
It is preferable that the binarizing step of the image signal processing method for glass fragmentation test includes a first binarizing step for binarizing the tone image signals into cracked portions and fragmented portions based on a threshold value image obtained by modifying threshold values according to brightness of a background in the tone image, a second binarizing step for examining a tone distribution in a plurality of directions in a certain region around a noteworthy pixel of the tone image and for performing binarization so as to recognize the noteworthy pixel as a cracked portion when in at least one direction of the tone distribution, a central portion is dark and both end portions are bright, and a binarized image combining step for combining the image signals binarized in the first binarizing step and the image signals binarized in the second binarizing step. Such binarization may be applied to the plate-shaped glass fragmentation testing methods, the plate-shaped glass fragmentation testing devices or another one.
By this binarization, the first binarizing step based on a threshold value image obtained by threshold values according to brightness of the background in the tone image, and the second binarizing step based on the minute tone distribution in the plurality of direction in the certain region around the noteworthy pixel can be performed, and the results of both binarization can be combined to binarize the tone image signals in more optimum fashion, obtaining the binarized image signals in an effective way without failing detection of a cracked portion. As a result, operations, such as calculating the fragments, can be performed more accurately, and the fragmentation test can be carried out with high precision.